1,016 research outputs found
Distributed Markovian Bisimulation Reduction aimed at CSL Model Checking
The verification of quantitative aspects like performance and dependability by means of model checking has become an important and vivid area of research over the past decade.\ud
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An important result of that research is the logic CSL (continuous stochastic logic) and its corresponding model checking algorithms. The evaluation of properties expressed in CSL makes it necessary to solve large systems of linear (differential) equations, usually by means of numerical analysis. Both the inherent time and space complexity of the numerical algorithms make it practically infeasible to model check systems with more than 100 million states, whereas realistic system models may have billions of states.\ud
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To overcome this severe restriction, it is important to be able to replace the original state space with a probabilistically equivalent, but smaller one. The most prominent equivalence relation is bisimulation, for which also a stochastic variant exists (Markovian bisimulation). In many cases, this bisimulation allows for a substantial reduction of the state space size. But, these savings in space come at the cost of an increased time complexity. Therefore in this paper a new distributed signature-based algorithm for the computation of the bisimulation quotient of a given state space is introduced.\ud
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To demonstrate the feasibility of our approach in both a sequential, and more important, in a distributed setting, we have performed a number of case studies
Efficient CTL Verification via Horn Constraints Solving
The use of temporal logics has long been recognised as a fundamental approach
to the formal specification and verification of reactive systems. In this
paper, we take on the problem of automatically verifying a temporal property,
given by a CTL formula, for a given (possibly infinite-state) program. We
propose a method based on encoding the problem as a set of Horn constraints.
The method takes a program, modeled as a transition system, and a property
given by a CTL formula as input. It first generates a set of forall-exists
quantified Horn constraints and well-foundedness constraints by exploiting the
syntactic structure of the CTL formula. Then, the generated set of constraints
are solved by applying an off-the-shelf Horn constraints solving engine. The
program is said to satisfy the property if and only if the generated set of
constraints has a solution. We demonstrate the practical promises of the method
by applying it on a set of challenging examples. Although our method is based
on a generic Horn constraint solving engine, it is able to outperform
state-of-art methods specialised for CTL verification.Comment: In Proceedings HCVS2016, arXiv:1607.0403
Verification of diagnosability based on compositional branching bisimulation
This paper presents an efficient diagnosability verification
technique, based on a general abstraction approach.
We exploit branching bisimulation with explicit
divergence (BBED), which preserves the temporal logic
property that verifies diagnosability. Furthermore, using
compositional abstraction for modular diagnosability verification
offers additional state space reduction in comparison
to the state-of-the-art techniques
A Team Based Variant of CTL
We introduce two variants of computation tree logic CTL based on team
semantics: an asynchronous one and a synchronous one. For both variants we
investigate the computational complexity of the satisfiability as well as the
model checking problem. The satisfiability problem is shown to be
EXPTIME-complete. Here it does not matter which of the two semantics are
considered. For model checking we prove a PSPACE-completeness for the
synchronous case, and show P-completeness for the asynchronous case.
Furthermore we prove several interesting fundamental properties of both
semantics.Comment: TIME 2015 conference version, modified title and motiviatio
INCREMENTAL FAULT DIAGNOSABILITY AND SECURITY/PRIVACY VERIFICATION
Dynamical systems can be classified into two groups. One group is continuoustime systems that describe the physical system behavior, and therefore are typically modeled by differential equations. The other group is discrete event systems (DES)s that represent the sequential and logical behavior of a system. DESs are therefore modeled by discrete state/event models.DESs are widely used for formal verification and enforcement of desired behaviors in embedded systems. Such systems are naturally prone to faults, and the knowledge about each single fault is crucial from safety and economical point of view. Fault diagnosability verification, which is the ability to deduce about the occurrence of all failures, is one of the problems that is investigated in this thesis. Another verification problem that is addressed in this thesis is security/privacy. The two notions currentstate opacity and current-state anonymity that lie within this category, have attracted great attention in recent years, due to the progress of communication networks and mobile devices.Usually, DESs are modular and consist of interacting subsystems. The interaction is achieved by means of synchronous composition of these components. This synchronization results in large monolithic models of the total DES. Also, the complex computations, related to each specific verification problem, add even more computational complexity, resulting in the well-known state-space explosion problem.To circumvent the state-space explosion problem, one efficient approach is to exploit the modular structure of systems and apply incremental abstraction. In this thesis, a unified abstraction method that preserves temporal logic properties and possible silent loops is presented. The abstraction method is incrementally applied on the local subsystems, and it is proved that this abstraction preserves the main characteristics of the system that needs to be verified.The existence of shared unobservable events means that ordinary incremental abstraction does not work for security/privacy verification of modular DESs. To solve this problem, a combined incremental abstraction and observer generation is proposed and analyzed. Evaluations show the great impact of the proposed incremental abstraction on diagnosability and security/privacy verification, as well as verification of generic safety and liveness properties. Thus, this incremental strategy makes formal verification of large complex systems feasible
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